Sleep mask



FIG. 1 is a perspective view of a sleep mask showing my new design;

FIG. 2 is another perspective view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof;

FIG. 6 is a right side elevational view thereof;

FIG. 7 is a top plan view thereof;

FIG. 8 is a bottom plan view thereof; and,

FIG. 9 is an enlarged view of portion 9 shown in FIG. 2 .

The dot-dash broken lines represent the boundary of the enlarged portion and form no part of the claimed design. 

CLAIM The ornamental design for a sleep mask, as shown and described. 